If one watch should have "all" I need, it would be:
1. Extremely small ! Just HATE big chunky watches as they are useless out there, where lines and board edges and fins etc can get caught, and when riding you want to feel free with as little wetsuit and excess gear as possible.
2. Time displayed ALWAYS, no matter what other mode you are into (which in my case would be #3).
3. Countdown for video/timelapse timing when using a kitecam, or for icy winthersession where you want to time the triggering of the Lewis Hunting Response perfect without "screaming" pain, nor shortened sessions.
4. "Silent" GPS, meaning it simply logs everything in a data file (no need for maps etc), so you can go home and look at the exact wind direction and shifts, and your upwind angles and tack efficiency and up-downwind vmg's if on race or racelike gear.
I have never had use for anything else but that.
Above dont exist yet I think, so I use a very small extremely shock resistant for 1+2+3, and then a GT-31 on my upper arm when I want to log tracks too.
Would be better to have it all in one, true, but havent seen that yet.
Of course you could also have a temperature measurement and windmeter etc etc (I HAVE one with both actually, and a lot more), but they will NEVER fit into the most important demand, namely point #1 - EXTREMELY small thank you
And I could be worried about battery life for such an almost "perfect" watch too, as my GT31 can hold for more than 20 hours logging.
10 hours would suffice, as 8 hours is my typical max session length.
So I think the battery life is the problem.
My normal 1+2+3 watch has a battery lifetime between 10 and 15 years.
With a GPS you have to charge your watch quite often instead of course.
And if you use it as your everyday watch too (well, at least every other day, when you are on the water), it does not make sense to have a watch that might run out of current suddenly.
At least the GPS function should disable automatically long before the time runs out so to speak (at least a full workday), to be of any daily use whatsoever IMO.
Not that easy, maybe not even possible, to satisfy these demands really